A variety of products exhibit a tendency to release or emit gas after they have been placed within a sealed package, container or vessel. For example, roasted coffee beans have a tendency to release carbon dioxide. Some of that carbon dioxide is typically released from the beans after they are placed and sealed within a package or container. Such packages or containers are typically constructed from cardboard, plastic, polyethylene, polyolefin or other materials. As gas is released from coffee beans within the sealed container, the gas pressure builds, resulting in a tendency for the walls of the container to expand outwardly. Depending upon the internal gas pressure and the rigidity and burst strength of the container, the results of building internal gas pressure can range from a simple pressurization of the container, to an expansion of the container walls outwardly, to ultimately a bursting of the container. Where the walls or ends of the container are sufficiently strong to prevent a rupture, the build up of gas causing a bulge or expansion of the container's exterior surfaces makes the container unattractive from the perspective of the consumer, who often equates an expanding container with spoiled product. Containers having walls that have expanded outwardly also present difficulties for retailers who attempt to maximize the use or retail shelf space.
To accommodate the build up and evolution of gases in such circumstances, others have proposed the placement of pressure activated relief valves on the surface of the packaging or container. Initially, pressure activated valves used in applications such as those described above were relatively simplistic in nature and were designed primarily to allow gas built up within the container to be released. The ability for the valve to function as a “one-way” valve to prevent an ingress of air from the exterior environment into the sealed packaging was often somewhat of an incidental feature. However, over time, it became apparent that not only was it desirable to allow the build up of gas within the sealed container to escape, but that it was in many instances important to prevent the ingress of exterior air back through the valve into the container. It was appreciated that the ingress of air into the sealed container would not only introduce oxygen of the container, but that it could also introduce water vapour and/or bacteria and/or spores, etc. that could cause fungal growth or spoilage. As a result, the integrity and ability of such valves to function as one-way valves was enhanced, to the point where valves of relative high integrity were created that would allow for the release of built up pressure with a sealed container, while at the same time preventing or limiting the ingress of atmospheric air back in through the valve and into the interior of the container. An example of such a valve is described in U.S. Pat. No. 6,663,284, dated Dec. 16, 2003.
Unfortunately, as the integrity and effectiveness of one-way valves in the nature of those described above increased, a side effect of their enhanced functionality has become apparent. One such side effect occurs when sealed containers containing such valves are transported under conditions of high temperature and/or low pressure. For example, products that are transported by air freight are typically exposed to low pressures that may be present in the cargo holds of airplanes. Under such circumstances, when the sealed containers are exposed to a low pressure environment during flight, the gas pressure within the containers will exceed that of the surrounding atmosphere, resulting in an expulsion of the gas from within the container through the one-way valve. The expulsion of gas from the container will tend to continue until the interior and exterior pressures have generally equalized. As the airplane descends and the exterior atmospheric pressure increases, the one-way valve on the container tends to close, preventing the ingress of atmospheric air back into the container. By the time that the airplane lands, there can have developed a significant vacuum state within the container. Once again, depending upon the nature of the container's walls, the end result may be a collapsing of the container walls inwardly. Where the walls do not collapse inwardly, the establishment of a vacuum within the container results in an immediate rush of air into the container when it is opened by a consumer. Where a container's walls have collapsed inwardly, the same concerns arise as with the above described case of the container having walls that have expanded. In addition, the sudden rush of air in the container when it is opened that results from the establishment of a vacuum state can have deleterious effects on the product stored therein. For example, in the case of roasted coffee, should a consumer open a package that is in a vacuum state the rush of air in the container when it is opened will expose the coffee to oxygen, which can cause oxidation of the coffee, often giving it a bitter taste.
It will be appreciated that the same vacuum state can be established within containers that are shipped by truck or rail, where the truck or rail car passes through areas of significant elevation changes (for example, mountainous regions). In addition, in situations where product is transported in hot environments, the product could be exposed to elevated temperatures which would have the result of increasing the gas pressure within the containers and forcing gas through the one-way valve. When the environment within which the containers are being shipped returns to a more traditional temperature, the resulting reduction of the gas pressure within the container, in conjunction with the operation of the one-way valve, can establish a vacuum situation.